Correction of leg-length discrepancy among meat cutters with low back pain: a randomized controlled trial

BACKGROUND: The etiology of non-specific low back pain (LBP) is complex and not well understood. LBP is common and causes a remarkable health burden worldwide. Leg-length discrepancy (LLD) is potentially a risk factor for development of LBP, although this relationship has been questioned. Yet only one randomized controlled study (RCT) has been performed. The objective of our study was to evaluate the effect of insoles with leg-length discrepancy (LLD) correction compared to insoles without LLD correction among meat cutters in a RCT-design. METHODS: The study population consisted 387 meat cutters who were over 35 years old and had been working 10 years or more. The LLD measurement was done by a laser ultrasound technique. All workers with an LLD of at least 5 mm and an LBP intensity of at least 2 on a 10-cm Visual Analog Scale were eligible. The LLD of all the participants in the intervention group was corrected 70%, which means that if the LLD was for example 10 mm the correction was 7 mm. The insoles were used at work for eight hours per day. The control group had insoles without LLD correction. The primary outcome was between-group difference in LBP intensity. Secondary outcomes included sciatic pain intensity, disability (Roland Morris), RAND-36, the Oswestry Disability Index, physician visits and days on sick leave over the first year. We used a repeated measures regression analysis with adjustments for age, gender and BMI. The hurdle model was used for days on sick leave. RESULTS: In all, 169 workers were invited and 114 (67%) responded. Of them, 42 were eligible and were randomized to the intervention (n = 20) or control group (n = 22). The workers in the intervention group had a higher improvement in LBP intensity (− 2.6; 95% confidence intervals − 3.7 – − 1.4), intensity of sciatic pain (− 2.3; − 3.4 – − 1.07) and RAND-36 physical functioning (9.6; 1.6–17.6) and a lesser likelihood of sick leaves (OR -3.7; − 7.2 - -0.2). CONCLUSIONS: Correction of LLD with insoles was an effective intervention among workers with LBP and a standing job. TRIAL REGISTRATION: ISRCTN11898558. Registration date 11. Feb 2011. BioMed Central Ltd.